1. Field of the Invention
The subject invention relates to a passively activated safety needle assembly to prevent accidental needle sticks.
2. Description of the Related Art
Many medical procedures require the use of a sharply pointed metallic needle cannula for obtaining a sample of fluid from a patient or for delivering a fluid to the patient. The sharply pointed metallic needle cannula must be handled carefully to avoid an accidental stick with the point of the needle cannula. An accidental stick with a sterile needle cannula is painful and can leave an open wound that is subject to infection. An accidental needle stick with a used needle cannula can transmit disease.
Safety shields are employed widely in the health care industry to eliminate or reduce the risk of accidental needle sticks. Safety shields have taken many forms, including shields that telescope along the needle cannula from a proximal position to a distal position. The distal tip of the needle cannula is exposed for use when the shield is in the proximal position. However the pointed tip of the needle cannula is covered when the shield is in the distal position.
Some shields are large and telescope over a syringe, needle holder or other medical implement. Some such large shields also include coil springs to propel the shield distally. The spring typically is locked in a collapsed condition around proximal portions of the medical implement when the shield is retained in the proximal position. An actuator is triggered after use of the medical implement to release the spring and drive the shield distally into a shielding disposition around the needle cannula.
Other shields are much smaller and are configured to telescope only along the needle cannula. The shield in these prior art devices may be connected to the syringe or the needle hub by a tether or a linked array of hinged arms to limit the range of movement of the shield relative to the needle cannula. Thus, the shield can be moved distally into surrounding relationship with the tip of the needle cannula. However, the tether or hinged arms prevent the shield from sliding completely off the needle cannula. Some shield assemblies of this general type include a spring mechanism for assisting a portion of the distal movement of the shield along the needle cannula. A shielding assembly of this general type is shown in U.S. Pat. No. 5,348,544 which is assigned to the assignee of the subject invention. The shielding assembly shown in U.S. Pat. No. 5,348,544 requires the user to initiate shielding by exerting digital pressure on one of the hingedly connected arms. This initial digital pressure will be resisted by the spring. However, after a certain range of movement, the hingedly connected arms will be positioned such that the spring assists the distal movement of the shield. The needle shielding device shown in U.S. Pat. No. 5,348,544 is very effective. However, a device with passive or automatic shield actuation could provide certain advantages over the prior art.
The subject invention is directed to a passively activated safety needle assembly with a shield configured for sliding movement along a needle cannula. The needle cannula comprises a proximal end and a distal end that is sufficiently pointed for penetrating skin and adjacent tissue of a patient. The proximal end of the needle cannula may be mounted in a hub. The hub may be molded from plastic and may be configured for mounting to a syringe, a needle holder or other medical implement.
The shield of the passively activated safety needle assembly may be slidably movable along the needle cannula from a proximal position substantially adjacent the hub to a distal position for shielding the tip of the needle cannula. The needle shield may include a spring latch formed from a metallic material and biased against a lateral side of the needle cannula as the shield moves from the proximal position toward the distal position. The spring latch may be dimensioned and configured to overlie the distal tip of the needle cannula when the shield reaches its distal position.
The passively activated safety needle assembly of the subject invention further comprises connection means for limiting movement of the shield along the needle cannula. The connection means may comprise a flexible tether or a plurality of hingedly articulating arms that can move from a collapsed condition to an extended condition. The connection means is in the collapsed condition when the shield is in its proximal position relative to the needle cannula. However, the connection means is in a fully extended condition when the shield has advanced into shielding disposition around the tip of the needle cannula.
The connection means may comprise a distal end that is articulated to the shield and a proximal end that is articulated to or near the needle hub. More particularly, the proximal end of the connection means may be articulated directly to the needle hub. Alternatively, the proximal end of the connection means may be articulated to a base which in turn is connected securely to the needle hub.
The passively activated safety needle assembly of the subject invention further comprises a biasing means for urging the shield from the proximal position to the distal position. The biasing means may comprise a torsion spring mounted between a plurality of hingedly connected arms of the connection means. Alternatively, the biasing means may comprise a coil spring that surrounds the needle cannula at locations between the shield and the needle hub. The biasing means is disposed and configured for having stored energy when the safety shield is in its proximal position. Additionally, the biasing means is configured relative to the shield and the connection means such that the stored energy will urge the shield distally at all points along the range of movement of the shield. Thus, the biasing means is configured and disposed for urging the shield distally even when the shield is in its extreme proximal position. Accordingly, the biasing means avoids the need to initially exert digital pressure on the shield or on a hinged arm to start the shield moving toward the distal shielding position.
The passively activated needle assembly of the subject invention further comprises a safety cap that is removably engaged over the needle cannula prior to use. The safety cap may be formed from a rigid plastic material and may be dimensioned to cover the entirety of the needle cannula from the distal end to the proximal end. Proximal portions of the safety cap may be dimensioned for removable frictional engagement over the needle hub and/or over any base that may be provided to mount the connection means on the hub. A notch or slot may extend distally from the proximal end of the safety cap a sufficient distance for receiving the hingedly connected arms or other such connection means. The safety cap performs two functions. First, the safety cap prevents accidental sticks with the needle cannula prior to use. Additionally, the safety cap releasably holds the safety shield in a proximal position.
The shield of the subject invention initially is in its proximal position on the needle cannula with the connecting means in the collapsed condition and with the stored energy in the biasing means. The safety cap then is mounted over the needle cannula and over the shield sufficiently for removable frictional engagement of the safety cap with either the needle hub or with the base to which the connection means is articulated. This initial positioning of the safety shield and the safety cap is carried out at the place of manufacture and does not require any action by the health care worker.
A health care worker may mount the passively activated safety needle assembly to a syringe, needle holder or other medical implement in a conventional manner. This mounting may involve the mere axially movement of a Luer tip into a Luer receptacle of the needle hub. Alternatively, the needle hub of the passively activated safety needle can be threaded into engagement with a Luer collar.
The health care worker then grips the connection means and the syringe or needle holder between a thumb and forefinger. This engagement ensures that the shield will remain in a proximal position. The health care worker then grabs the safety cap with the other hand and pulls sufficiently to disengage the safety cap. The required pulling force is approximately the same as the pulling force to separate any safety cap from a needle assembly in the prior art. The health care worker then continues to exert digital pressure on the connection means and urges the exposed distal tip of the needle cannula into a targeted location on the patient for obtaining a fluid sample or for delivering a fluid drug to the patient. After the needle cannula has been placed in communication with the patient, the health care worker may release the grip on the connection means. This release of the connection means enables the spring to drive the safety shield distally. The distal movement of the safety shield along the needle cannula terminates when the distal end of the safety shield contacts the skin of the patient.
The needle cannula is removed from the patient after an appropriate volume of liquid has been withdrawn or after an appropriate dosage of a drug has been administered. Proximal movement of the needle cannula associated with the withdrawal of the needle cannula from the patient permits the safety shield to be driven further in a distal direction by the biasing means. Thus, the distal end of the safety shield will remain in contact with the skin of the patient as the needle is moved proximally relative to the patient. Upon complete removal of the needle cannula from the patient, the biasing means will advance the shield into its full shielding condition around the distal tip of the needle cannula. The safely shielded needle then can be separated from the syringe or needle holder and discarded into an appropriate sharps receptacle. Alternatively, the entire needle assembly and needle holder may be discarded.
The health care facility occasionally is a hectic environment, and fluids near the patient may make medical implements slippery. Thus, the potential exists for the health care worker to drop the needle assembly before use. Inadvertent dropping of the passively activated safety needle will immediately cause the shield to be propelled by the spring into its distal shielding position around the needle cannula. Hence, accidental sticks are avoided even in situations where the unused needle cannula is accidentally dropped.